The technical function of switching converters is to convert voltages from a first voltage level to at least one second voltage level. This may be from a low voltage (e.g., 13.5 V) to a high voltage (e.g., 33 V). Furthermore, there are voltage converters which convert a high voltage (e.g., 33 V) into a low voltage (e.g., 6 V).
The voltage converters usually have an essentially fixed working clock, such as 2 MHz.
As a result of the technical function of the voltage converter, parasitic, electromagnetic interferences are generated. These interferences are partially directly related to the working clock. A switching converter operated at a working clock of 2 MHz generates harmonic interferences at distances of 2 MHz. The amplitude of the individual interference sources and the maximum interfering frequency are dependent on the configuration of the switching converter.
The interferences often make additional measures necessary so that, for example, control units in which the switching converters are used, meet statutory requirements or customer requirements with respect to the (electromagnetic) emissions.
One of a variety of measures is the controlled variation of the working clock. This variation is usually referred to as jitter. The variation of the clock is usually set to the maximum frequency variation which the switching converter control unit is still able to reasonably process. The idea behind this is that a maximum frequency variation causes a maximum reduction in the emission.
One disadvantage of this technique is that only a partial optimization (a frequency range) of the emissions takes place here, and not all issues, such as the additional frequency range or the radio reception in the immediate surroundings of such switching converters, are taken into consideration.
The interferences by switching converters according to the related art usually do not take place due to direct demodulation, but due to indirect demodulation via the intermodulation effect with the aid of an FM transmitter. There is also the effect that the switching converter emissions have “matching” frequencies and then, in combination with the superimposed spectrum of an FM transmitter, become (undesirably) audible due to a direct demodulation.